A metal building, generally, is a lightweight structure consisting of vertical steel columns, steel rafter beams bolted to the vertical columns and generally spaced from 20 to 30 feet apart. The rafter beams are generally sloped to provide positive drainage. Spanning the columns and rafter beams at sidewalls and roof are a series of light gauge sub-structural “z” or “c” sections bolted to the columns and rafter beams. These are generally on 4′ to 5′ spacing and run perpendicular to the columns and rafter beams, commonly known in the trade as purlins for roof support and girts for sidewall support.
Covering the structural system are ribbed, fluted, standing seam or profiled panels with alternating higher ribs and flat valleys or pans generally with high rib being 6″ to 24″ on center and valleys being 4″ to 18″ across the flat and of generally 26 gauge or 24 gauge sheet metal, creating a structural diaphragm when fastened to the substructural system. Such higher rib surface's lie substantially in an upper plane and the bottom valley or pan surfaces lie substantially in a lower plane spaced apart from the upper plane. The alternating top and bottom surfaces are interconnected by a series of webs extending parallel to the longitudinal axis of the formed panel diaphragm.
There are an infinite variety of shapes of such configurations commercially available. For simple reference refer to the top surface as being the top plane of the higher rib and base surface as being the lower plane of the low rib. The web being the connecting form of the two. The panels are generally attached to the aforesaid sub-structural members with generally a series of threaded screws, generally 12″ or less on center for the entire building length. Standing seam type roofing is attached to the sub-structural members by means of clips mounted on the sub-structural members. Certain installations of these panels separate the panels from the sub-structure by a distance of ½″ to 6″ to improve the thermal qualities of the roof and/or wall system. These assemblies are difficult and in some cases impossible to retrofit because of the problem of providing a solid, stable retrofit sub-framing system due to the compressibility of the insulating material or gap between the roof panel and sub-structure.
The design of metal building structures optimizes minimum weight materials to work in unison in meeting the building code requirements for wind, snow, ice and live loading for the many geographical location's exposure to the elements. In achieving that criteria, each component is engineered to meet the requirements of the codes.
In re-roofing of such structures, extreme attention is given to limiting imposition of further dead loads on the original structural design and yet to resist the full wind uplift requirements of multiple building codes.